The long term objective of this proposal is to develop a system for the reliable production of human monoclonal antibodies of high affinity and desirable isotype. The specific aims of this phase one proposal are intended to co-optimize two experimental systems: 1) The conditions for optimal in vitro stimulation of human splenic lymphocytes and 2) The specifics of the transfer to and restimulation of these human lymphocytes in severe combined immunodeficient (SCID) mice, so that high affinity IgG isotype human monoclonal antibodies can be more readily obtained. Specifically, we will 1) optimize the in vitro stimulation of human spleen cells for transfer to SCID mice; 2) optimize the conditions for in vivo antigen re-stimulation of these human spleen cells in SCID mice; and 3) determine whether additional human lymphoid tissue co-administered to the SCID mice or the use of double mutant SCID + beige mice can improve the antibody response of the grafted human spleen cells. Commercial applications of high affinity human monoclonal antibodies include passive immunization, tumor imaging, cancer immunotherapy and treatment of immunodeficiencies and allergies. Human monoclonal antibodies will alleviate much of the concern over infectious contaminants which arises when human antibodies are prepared from donor blood. They will allow the production of large quantities of well-defined antibodies. They should have longer half lives in patients that mouse antibodies. Desired effector mechanisms should be optimally stimulated because of the human origin and the control of isotype which monoclonal antibodies provide. Finally, they will minimize the problems encountered when administering a foreign antibody to humans, especially the human anti-mouse antibody (HAMA) response which has received much recent attention.